Enhancement in electroosmotic mixing in obstruction-laden microchannels

Abstract

The study presents a novel approach leveraging electroosmotic flow actuation within a charged obstruction-laden microchannel to improve mixing and transport. Through comprehensive numerical simulations that solve the coupled modified Poisson-Nernst-Planck and Navier–Stokes equations, and accounts for finite ion size and ionic cloud overflow across nano-conduits, we evaluate the mixing performance and flow throughput for various obstruction arrangements within a microchannel by quantifying outlet tracer distributions, scalar dissipation rate, finite-time Lyapunov exponent (FTLE) fields, and average outlet velocities. Our results reveal that charged obstructions outperform uncharged counterparts in mixing performance, while parallel obstruction arrangements yield higher velocities and better mixing as compared to alternate arrangements. Surface charge density at the surfaces plays a critical role, with both low and high values facilitate effective mixing, albeit higher surface charge densities promote increased flow rates. However, distinct mixing mechanisms are observed at the low and the high surface charge cases as revealed by FTLE analysis while moderate values of surface charge delineate poor mixing performance. Notably, subsequent obstructions with axially overlapped zones emerge as a critical design for efficient mixing, a configuration previously unexplored. Exploiting these findings, we propose a simplified channel design with fewer obstructions, achieving excellent mixing and higher throughput while ensuring fabrication simplicity. The flow characteristics qualitatively agree with previous experiments but uniquely explore the impact of axially overlapping subsequent obstructions on mixing. The present approach holds promise for the design of various porous microfluidic systems utilizing the existing fabrication technologies, with broad applicability in mechanotransduction and other biomedical devices.